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Big Fish With a Bigger Problem: The Yellowtail Tuna Faces Difficulty in More Acidic Oceans

Anthropogenic emissions of carbon dioxide (CO2) have resulted in increased concentrations of CO2 in ocean waters that subsequently result in ocean acidification. Bromhead et al. (2015) explored the effects of elevated CO2 levels on the development of yellowfin tuna, Thunnus albacares in their March 2015 Deep-Sea Research article. Tuna represent some of the largest predators in the ocean, and cover vast expanses across several of the earth’s oceans—meaning the effects of ocean acidification could have ramifications for the species and their ecosystems around the world. The researchers found that ocean acidification levels have a strong negative effect on growth, hatch time, and larval survival in the experimental trials. These findings show that future ocean conditions may reduce the survivability of this fish in the future and lead to drastic marine ecosystem changes—as well as affect fishing practices by humans around the world that currently depend on yellowtail as a main source of food.

The experiments, measured three variables across two trials—the time it took for eggs to hatch after fertilizations, the growth of tuna larvae, and their survival rates. The researchers conducted their experiments in a controlled environment at the Achotines Laboratory, belonging to the Inter-American Tropical Tuna Commission, in Panama. They tried to replicate natural conditions, and controlled eight tanks to four different ph levels (6.9, 7.3, 7.7, and 8.1) designed to reflect projections for future ocean acidities from the Hamburg Ocean Carbon Cycle by Ilyina et al. (2013).

In the first trial, all development three variables were strongly negatively affected by both CO2 treatments. The second trial saw an increase in time taken for eggs to hatch, but there was no clear relation established between larval survival and larval growth was only statistically affected at the highest pCO2 concentration. The experiment acknowledged, however, that there was a discrepancy between trails due to likely “unstable ambient conditions” in the second trial, and that future trials and/or studies were necessary to establish clearer results. When the results from both trials are taken into account, there enough concern to warrant continued research, as many marine ecosystems in the open ocean are dependent on the predation by yellowfin tuna of smaller fish for maintaining a natural equilibrium between predators and prey.

This study is important for economic reasons as well. Yellowfin tuna fisheries are responsible for providing a large portion of the commercial seafood industry’s fish stock, along with skipjack, bigeye and albacore. While fishing practices already reduce yellowfin tuna populations more and more with high demand and a growing global population, if there is any evidence that ocean acidification resulting from anthropogenic climate change reduces or threatens tuna populations, action will be necessary to protect the species, and the people that depend on it for food.